1. Field of the Invention
The present invention relates to a motor driving technique, and particularly to a control technique for the rotational speed of a motor.
2. Description of the Related Art
It is known that, when a motor such as a DC motor or a spindle motor is rotated, back electromotive voltage occurs in the motor according to its rotational speed (e.g., see Patent Document 1). Heretofore, a bridge control method has been used in which the back electromotive voltage is detected and used to control the rotation of a motor (e.g., in a cassette tape device, etc.). However, other methods using Hall sensors or speed sensors are typically employed for the reason that a method using back electromotive voltage has various disadvantages such as poor voltage use efficiency, changes in the resistance of the motor coil according to the temperature, and poor precision. However, there is still satisfactory usage value in such a method using back electromotive voltage in an arrangement that does not require high precision.
[Patent Document 1]
Japanese Patent Application Laid Open No. 2000-166285